


if we were to hold on

by martialartist816



Category: Shingeki no Kyojin | Attack on Titan
Genre: Canon Compliant, First Time, Foursome, M/M, Sexual instruction, Switching, Voyeurism
Language: English
Status: Completed
Published: 2021-01-03
Updated: 2021-01-03
Packaged: 2021-03-13 13:55:12
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 8,398
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28529547
Author URL: https://archiveofourown.org/users/martialartist816/pseuds/martialartist816
Summary: Eren and Armin find Reiner and Bertholdt together and wonder what they can do to be that close.
Relationships: Armin Arlert/Eren Yeager, Reiner Braun/Bertolt Hoover
Comments: 3
Kudos: 138





	if we were to hold on

**Author's Note:**

> **slight warning:** the four of them use the terms "man" and "woman" to describe top versus bottom. this is not accurate terminology, but as the plot revolves around Eren and Armin not knowing much about sex, Reiner and Bertholdt try to describe it as simply as possible

Eren and Armin have a special friendship. Their bond runs deep like siblings, but much different, much more than that. After all, siblings don’t do the things they do.

Their first kiss had been innocent enough. It was shortly after Armin’s grandfather had died, when Armin woke from a nightmare with clammy skin and a racing heart. Eren was there beside him, eyes wide as he watched Armin come back to his senses. The fear and the grief clung to him for minutes after he woke, and Eren, in his simple and valiant way, tried to comfort him with a kiss. The peck on the lips worked. Armin felt safer with Eren beside him, and they both fell back asleep clinging to each other like tangled branches.

That kiss had been the first of many, an opened floodgate in the frantic and lonely hearts of two boys in their early teens. They kissed whenever they had a moment alone together—in alleyways, under the covers, in the river when they bathed. It was comfortable. It felt right. Even so, something about sneaking away to kiss like married moms and dads do seemed private somehow. Armin once used the word “shameful,” and Eren got all huffy about it, though he kind of did, kind of didn’t understand why Armin was right. So they kept themselves, their evolving friendship, out of sight, a secret not even Mikasa was privy to.

A few weeks after joining the training corp, Armin woke up with a tent in his pants. Mortified, he turned away from Eren, only to have a hand wrap around his arm and pull him back.

“I get like that too,” Eren whispered harshly so no one else in the barracks could hear. He lifted their shared blanket, and Armin saw proof of Eren’s word, a sharp jut between his hips.

“We match,” Armin said with breathy awe.

Before the morning bugle cawed their signal to get out of bed, Eren and Armin touched themselves while raptly focused on the other’s hand, the other’s body. At some point, Armin tipped forward to kiss Eren to keep himself quiet, and they kept kissing until they reached climax. When they were done, their faces were stained pink, and there was a mess in the sheets. There was also a newfound electricity buzzing between them, a low hum that followed them around and sizzled brightly whenever they were alone together.

It was still their secret, but it was also more. It was something special they shared with each other that defied the limits of friendship and family and whatever other bonds tie two people together in this beautiful, cruel world.

Late afternoon is usually the best part of the day. Daily tasks and drills are finished, and the promise of a good dinner gets people into high spirits. It’s also the time of day that no one is really paying attention to the trainees, so Eren and Armin take the golden opportunity to sneak off somewhere away from people and indulge in each other’s bodies, quick to ignite and insatiable as they are.

The stables are a ways off from the dining hall where everyone has gathered for the meal, so as long as they don’t mind the pawing and nickering of some four-legged companions, it’s the perfect spot. Eren dashes around to the back of the barn, fingers laced with Armin’s, their smiles mirrors of each other.

“Eren,” Armin giggles. “They’re going to start serving soon.”

“We’ll make it quick,” Eren promises, ducking his head around stable doors to find one not in use.

“You always say that, and it’s never quick,” Armin complains, but he makes no move to detach his hand from Eren’s as he’s dragged around. “They’ll run out of potatoes by the time we get back.”

Eren halts his search abruptly and turns around. His hands cup both of Armin’s cheeks, and he knocks their foreheads together clumsily but cutely before kissing him deeply. “I’m hungry for something else anyway.”

He always manages to summon Armin’s blush with his words. Eren is shameless like that, and Armin loves him more for it. Whispered promises and romantic gestures such as these make Armin feel wanted—Eren makes him feel hot, all over, inside and out.

“Okay,” he agrees, eyes fixed on Eren’s lips when they leave his mouth. Eren flashes a beautiful smile, and he’s about to take Armin’s hand again to lead him deeper into the barn when a sound makes him stop short.

They both hold their breath and wait for a superior officer to find and scold them, the silence deafening. But then there’s another noise, a bit more distinct than the last, and Eren swivels his head to locate the direction it came from.

Wordlessly, he gestures for Armin to follow as he tip-toes toward the other side of the barn, his feet barely shifting the straw scattered on the ground. The noise gets clearer as they creep closer to whatever it is, until they’re rounding the corner where the back of the barn opens up to a pasture.

A distance away, there’s a tree with two figures pressed together against it. The sounds are coming from them, and it takes seeing the two of them together that makes it obvious the sounds have been their voices, hushed and desperate.

Eren and Armin don’t know what they’re looking at right away. They’re just far enough away to make out the familiar faces of Reiner and Bertholdt, but they’re in an odd position. Bertholdt is trapped between Reiner and the tree, his cheek and palms pressed to the bark, and his eyes appear closed. Reiner stands behind him with no room between them, and his body jerks in an almost-familiar way that has heat pooling in Eren and Armin’s bellies. Reiner and Bertholdt’s uniform pants are pushed down to their knees, the bare skin of their thighs slick with sweat.

“What do you think they’re doing?” Eren asks after a long, stunned silence.

Armin can’t tear his eyes away despite the fact that he feels like he shouldn’t be watching. He somehow intrinsically knows this is like what he and Eren do together, and that it’s supposed to be private.

When Armin doesn’t answer, Eren turns to him, ears pink. His whole body is alight with want and curiosity. Armin knows everything, so Eren eagerly awaits his explanation. Across the field, Bertholdt sounds like he’s feeling really good. Maybe Armin can tell Eren why that is. Maybe they can try for themselves.

“Armin,” Eren says, voice low. He takes Armin’s hand and guides it to the front of his pants where he’s already solid. He’d been excited for this long before he got to sneak away with Armin, and watching their friends doing something strange like that is making him so hot he’s almost dizzy.

Armin gasps and finally pulls his gaze from Reiner and Bertholdt to look down at his hand. His fingers rub at Eren’s cock through his already tight pants, mentally putting the pieces together.

“I think Reiner is inside him,” Armin says, and hearing it out loud sends arousal zipping down his spine. His knees feel weak just thinking about it, how it must feel if it’s forcing such sounds out of their normally stoic friends.

“H...How?” Eren asks, distracted by Armin’s fingers working the fly of his pants open.

Armin strokes him when he’s out, and Eren puts his hands on Armin’s shoulders to steady himself as he rocks in and out of his fist. The motion is strikingly similar to what Reiner is doing, what Bertholdt is apparently loving.

“One time, I was running home for dinner, but I was late,” Armin starts, pausing to lick his lips. Eren follows the movement of his tongue with his eyes. “I didn’t want my grandfather to be angry, so I tried to find a shortcut through an alley. I heard sounds like… like the ones B-Bertholdt is making right now, and I found a man and a woman together. The man pinned the woman to the wall, and he was standing between her legs. Her skirts were lifted high enough, I could see… The man stuck his—stuck himself into the woman.”

“Holy shit, Armin…” Eren breathes. Armin swipes over the moisture beading at the tip of Eren’s cock. There’s so much coming out today. “Can we do that? If it feels so good that they’re making sounds even louder than we do when we use our hands?”

“I don’t know if we can, Eren,” Armin says, uncertain. They’re standing so close that Eren’s cheek presses Armin’s temple. Sweat collects under their clothes, and they’re already panting into the warm summer air. “It’s what people do to have babies, and men can’t have babies. We don’t have the same parts as a woman, somewhere that’s… receptive for a man.”

“But they’re doing it.” Eren nods to Reiner and Bertholdt and gets mezmorized all over again. Reiner’s hands are on Bertholdt’s hips, and their bodies move so perfectly in sync it’s like they’re one person. Reiner is inside of him. If just Armin’s hand feels amazing, Eren wants to know what it’s like to be enveloped entirely by someone else’s body. “Do you think Bertholdt has—”

“He’s not a woman,” Armin cuts in, and then he flushes and buries his face in Eren’s shoulder. “I saw him in the showers once.”

“Then…” Eren trails off, looking away from their friends and ducking his head to nuzzle Armin’s hair. It hurts his brain to think of a way to make it work, but his body is ahead of him, brain muddled like it’s filled with cotton. “Let’s try to copy them.”

Armin backs up a bit to look at Eren, searching his eyes. Eren is so hard in his hand, and Armin is hard in his pants. It’s hot and muggy in this barn, and they’re wearing too many clothes. Armin wants Eren and will take as much of him as he’s allowed, as much as he’s able. It’s no surprise that Reiner and Bertholdt share a bond that’s like theirs, special and dynamic and—now—intimate. They’re as close as friends can be, and Armin wants that with Eren. It thrills him to think about there’s a way to be closer to Eren than he already is.

So he stands on his toes to peck Eren on the lips, then turns around. After undoing his pants and pushing them down as far as Bertholdt has his, Armin places his hands on the open barn door and looks back at Eren, whose mouth is gaping in arousal. They’re hidden enough that should Reiner or Bertholdt look this way, they can simply duck back into the barn without sacrificing their vantage point.

“Come closer,” Armin beckons quietly, and Eren’s mouth goes dry.

He steps forward, shuffling as best as he can with his pants around his knees, and mimics Reiner’s position. His hands find Armin’s hips, instinct telling him to pull Armin back until their bodies press together in the middle. Armin bends forward a bit, gasping when Eren’s cock slides against his exposed ass.

They don’t line up perfectly. Eren’s cock slips into the valley of Armin’s ass and rides up his lower back, dragging slick fluid wherever it goes. It feels like he’s doing something right though, because he rocks forward on instinct and groans at the sensation that blooms from his hips.

“You need to be lower,” Armin says, breathless. He knows they’re close to the mark, at the mercy of whatever it is his body is asking for. “Spread your legs a little.”

Eren does as much as he can manage with his pants still constricting him. He slides his feet apart until his hips are the same height as Armin’s, his shaft settled nice and warm against his ass.

“That’s it,” Armin gasps, and it sounds so sweet. He rocks back every time Eren pitches forward, and they’re starting to resemble Reiner and Bertholdt under that tree.

There’s only one place Eren could conceivably fit himself, and his knees nearly buckle when he realizes it. Of course. How could he have been so dumb? Eren pulls back a few inches and wraps a hand around the base of himself, angling downward just a little bit more. He can’t see where he’s aiming, but he knows when he finds it. Armin tenses up and moans, a high, quiet sound. Eren circles the rim with the head of his cock and sees stars. _There,_ his brain tells him. _You want to be in there._

He’s so wet, and he gets it all over Armin in his search for pleasure. He tries to push in, one hand holding himself in place and the other keeping Armin steady. Armin twitches and gasps, but there’s no give. Eren feels like he’s trying to press into a brick wall, but his head swims with how _close_ it feels to being right.

“Eren,” Armin moans shakily, reaching back blindly to hold Eren’s hip. He doesn’t pull him closer like Eren wants, but instead tries to push him away. “Eren, don’t. It’s not going to work without hurting.”

“But…” Eren glances over to where Reiner and Bertholdt are still going at it. Bertholdt doesn’t look like he’s in pain at all. But Eren doesn’t want to hurt Armin to get there.

“We’re missing something,” Armin says, sensing Eren’s hesitation. He looks back, pupils wide and eyelids lowered. His face is so red. “Please. Let’s just do it how we usually do it. I want to feel your hands on me.”

Despite everything in Eren’s body telling him to push forward, he backs up and spins Armin around. They move further into the barn, and Eren leans Armin against a bale of hay propped up next to the wall. He crowds in close, the necklace on his chest glinting against his sweat-soaked shirt, and kisses Armin like a starving man.

Armin’s arms fly around his neck, holding him close as they exchange kisses and hot breaths and each other’s tongues. Between them, their cocks slide and grind together, out in the open and so, so hot. Eren helps the friction find a rhythm, the image of Reiner’s jerky movements burned behind his eyelids. Armin rocks with him, and they find a tandem rhythm that’s both wild and focused, a singular goal on their minds.

Eren complies with Armin’s whispered request and puts his hands everywhere. He slides his fingers into Armin’s hair and messes it up like he’s not worried about having to look decent afterward. His other hand slides down Armin’s side, trails over his bare thigh and squeezes. Armin lets out sweet, hushed sounds into Eren’s mouth, eyes pinching shut as the pleasure mounts and mounts and comes to a head.

His muscles seize up when he releases, mouth hanging open and too useless to kiss back. They’re good at keeping quiet during this part, always afraid of waking the other boys or drawing unwanted attention to their well-used hiding places. Eren strokes Armin’s cheek until his breathing starts to slow, and then his brain is too muddled to think of anything but reaching his peak. His head drops forward until he’s resting on Armin’s shoulder, his hips giving their last few erratic thrusts before he spills between them with a soft groan.

Armin rubs his fingers up and down the back of Eren’s neck until he lifts his head back up. They’re both glistening with sweat, faces stained red with blush. Eren’s lips tug up in a wide grin, and Armin mirrors the expression with one of his own, dimples on display. Whoever moves first, it’s anyone’s guess, but they’re kissing again, lazy and blissful. And that’s all that matters.

They clean the mess with the insides of their shirts and fix their clothes. There’s nothing they can do about the sticky feeling all over their skin until later when the showers are open, but it’s a minor inconvenience that can be ignored until after dinner.

“Do you think they’re still at it?” Eren asks. Armin reaches up with both hands to make Eren’s hair look more or less how it did before they started. Eren returns the gesture, smoothing one hand down Amrin’s hair to tame it.

Armin leads Eren around the corner to peek beyond the barn door, up the hill to the tree. Eren hovers over Armin, his breath ghosting over his shoulder. Reiner and Bertholdt are still there, but they’ve separated and fixed their clothes. They both look calm, relaxed.

“We must have finished around the same time,” Armin notes. Eren laughs quietly.

“I still want to know how they managed it,” Eren states, his heart already set on it.

“You’re not thinking of…” Armin trails off, eyes following Eren as he marches out of the barn and heads for the tree. Curiosity getting the better of him, Armin follows.

Reiner and Bertholdt are in the middle of a conversation about mock battle formations, pretending to be casual as Eren and Armin approach.

“Aren’t you two supposed to be in the mess hall?” Reiner asks as a greeting.

“We’re all supposed to be,” Armin says before Eren butts in.

“We saw what you were doing.”

Bertholdt’s eyes go wide, but Reiner maintains a cooler expression, crossing his arms.

“What do you think you saw?” Reiner asks.

“Something secretive enough that you had to hide it,” Eren responds smugly. “We could tell Shadis what you were up to if you don’t—”

“You won’t be telling Shadis anything if I pummel you into the ground,” Reiner interrupts. Next to him, Bertholdt holds his hands up like he’s ready to hold Reiner back from a physical fight.

Armin steps in front of Eren and smiles amicably. The blush remains on his face, so it’s probably no secret that he and Eren were up to something very similar.

“He doesn’t mean to threaten you,” Armin says in Eren’s place. He pauses, then decides on a small risk, taking Eren’s hand and lacing their fingers together. They’re not like this in front of other people, but if Reiner and Bertholdt share the same relationship, Armin trusts them with his and Eren’s secret. “We want to learn from you.”

Reiner’s expression notably changes from aggressive indifference to mild surprise and amusement. Bertholdt still has the same worried look on his face. Reiner glances at their linked hands and relaxes his posture.

“Learn what?” he asks simply.

“How to be as close as you were,” Eren says.

Reiner regards them both for an extended moment, then shares a look with Bertholdt. They communicate silently between each other, which ends with Bertholdt placing a hand on Reiner’s shoulder and gently saying, “I’m okay with it if you are.”

“Alright,” Reiner says to Armin and Eren. “Next time you’re on barracks cleaning duty, we’ll join you there while everyone else is working.”

“Join us for what?” Eren asks indignantly.

Reiner snorts a laugh. “You want us to teach you, right? Better to show rather than tell.”

It’s nearly a week before Eren and Armin are assigned to clean the barracks as part of the trainees’ chores. It guarantees they’ll be alone for a few hours with a rare chance someone should decide to walk in on them. Twenty minutes into Eren milling around between bunks and Armin actually tidying a few things up, Reiner and Bertholdt walk in. Eren perks up, and a wave of anticipation washes through Armin’s body.

“Let’s use your bunk,” Reiner says after surveying the room. “More room over our heads.”

Eren and Armin exchange a look, then Armin leads them up to their bed. It’s spacious enough for the four of them, well away from the door and any wandering eyes that might pass by.

Armin settles by the foot of the bed with his legs crossed, and Eren sits next to him. Reiner and Bertholdt take their place across from them, and it feels just like the late nights they used to have chatting with their friends about the military and the walls and the rest of the world.

“How far have you two gone?” Reiner asks. Bertholdt busies himself with taking something out of his pocket and laying it to the side. It’s a plain bottle with the label rubbed off, a cork stopper in the top.

“How far?” Armin asks with a small voice. He feels terribly undereducated about all of this, but then again, he wouldn’t have had to ask for help if he knew what he was doing.

“With each other,” Reiner says with a hint of exasperation. “What parts have you touched? What do you usually do when you’re together?”

Armin can’t fight the blush fading into his cheeks. He glances at Eren, who’s just as embarrassed when faced with something he’s usually so confident about. That is, when he’s alone with Armin and taking the lead.

“Um, we mostly kiss,” Armin says, not looking at anyone. “We always start with that, and when it gets really, uh, heated, we use our h-hands on each other. Or lay down with one person on top and let our bodies do the work. Sometimes, if there’s time, we take our clothes all the way off and w-watch each other.”

“I told you they probably had no idea about any of this stuff,” Bertholdt says to Reiner. “They don’t exactly have access to the same kind of—”

“The same kind of what?” Eren asks. “We’re the same age as you are. How do _you_ know so much about it?”

“There were… books in our village,” Bertholdt answers, drawing his legs up and wrapping his arms around them. “Books about how two men can be together.”

“With pictures,” Reiner supplies with a smirk.

“Did you bring any?” Eren leans forward excitedly. “I want to see!”

“Eren…” Armin admonishes shyly.

“Those kinds of books are illegal, dumbass.” Reiner shoves at Eren’s head, messing up his hair. “Why the hell would we bring them to the training corp?”

“Reiner,” Armin sidetracks. “Asking us how far we’ve gotten implies there’s more, doesn’t it? Something like what we saw you and Bertholdt doing.”

“A man can be inside another man, but it’s not as easy as when you’re with a woman,” Reiner explains clinically. “Women have… measures for making it easier, so men have to improvise and accommodate.”

“It’s probably best to determine which one of you wants to be the ‘man’ this first time around, and which one wants to be the ‘woman’,” Bertholdt adds gently, looking a little flushed himself.

The roles come to mind when Armin remembers back to watching their friends in the pasture. Reiner had Bertholdt pinned, just like when Armin saw the man pinning the woman to the wall all those years ago. In that case, Bertholdt looked and _sounded_ rather happy to play the woman. Inside that barn, Eren tried to do the same to Armin, and Armin wanted to let him.

Eren looks at Armin with a bit of uncertainty. He wants Armin to make the call, since he’s smarter about things that come from books. As long as he’s with Armin, he doesn’t care what he’s doing.

“Sometimes, when Eren is laying on top of me, it feels really good to spread my legs and feel him between my thighs,” Armin confesses with a small smile. Eren gapes at him, having never known that despite how long they’ve been doing this.

“Called it,” Reiner says with a private glance to Bertholdt.

“Have you ever used your mouths on each other?” Bertholdt asks, ignoring Reiner. His voice is gentle, more patient than Reiner in a way that helps Eren and Armin relax a little more.

“I like kissing Armin,” Eren says clearly, like a declaration of love. He looks over to Armin, finding comfort in those sky-blue eyes that shine so brightly. “Kissing his mouth, or his soft cheeks. Sometimes his ears, when I want to hear him laugh.” He’s smiling when he says it, and Armin blushes as if that has been the most scandalous thing Eren has ever said to him.

“Wow, you two really are…” Bertholdt breathes, trailing off to shake his head and smile.

“Grossly adorable,” Reiner agrees, then he sighs. “But that’s not what we mean. We’ll just have to show you.”

Eren and Armin glance at each other, anticipation itching under their skin. It’s Armin who moves first, scooting himself closer to Reiner. After a brief hesitation, he peels off his shirt and lays it over the edge of the bunk. His shoulders and chest are pale and narrow, but with their vigorous training just beginning, he’s bound to fill out sooner rather than later.

“Lay on your back,” Reiner instructs, and Armin does, reclining back on the mattress between the three of them.

Eren watches in fascination as Reiner tugs Armin’s boots off. His fingers hook in Armin’s pants, and those are swiftly rid as well. Armin bends his legs to slide them out of his pants, and he lays bare and open with his feet planted to the bed. A twinge of possessiveness strikes Eren right in the chest. He’s the only one who can see Armin like this.

Armin catches his eye, upside down, and flashes a small but confident smile. Eren relinquishes his jealousy. They are here to learn, after all.

Reiner’s hands slowly trail up Armin’s thighs, his dry skin rasping over Armin’s like a whisper. When he reaches mid-thigh, Reiner coaxes them apart and leans down. Eren and Bertholdt both watch in awe as Reiner takes Armin’s soft cock in one hand and fits his mouth around him.

Armin gasps, and Eren does too. Reiner’s mouth is warm and wet, and his tongue wriggles against Armin’s shaft in a way that’s foreign but entirely incredible. He sucks his way down to the base, and when Armin starts to harden in his mouth, Reiner moves his hand away and lets it fill him as much as he can take.

With Armin’s breaths coming out shaky, Reiner drags his head up and down slowly, spreading his saliva and making the glide easier.

“That looks like it feels…” Eren says in a daze to no one in particular.

Bertholdt leans over to him, letting a large hand fall over the bulge forming in Eren’s pants. He hadn’t noticed he’s gotten hard already.

“It feels really nice,” Bertholdt says, rubbing him up and down. They’re both watching Armin as his chest heaves and his hips twitch. Reiner holds him in place with both hands, controlling the pace and the movement of his head and lips.

“Reiner, it’s…” Armin’s voice wobbles. “I’m leaking, but your mouth is…”

Reiner pulls off, his fist coming around Armin to replace his mouth as he speaks. His lips are shiny. “You can swallow it. It doesn’t taste that great, but it’s not going to kill you if you swallow.”

“Even when you finish?” Eren asks, enthralled.

“Even then. Makes for quick clean-up.” Reiner lowers himself back down, this time allowing Armin’s hips to jerk up into the heat of his mouth. Armin moans, not caring about being quiet when all his effort is put into not trembling out of his skin.

While he’s still distracted by the sight that is Armin gasping and tugging Reiner’s hair, Bertholdt cups his hand behind Eren’s neck and pulls him in. They rise up on their knees together, hips slotting into place, and Bertholdt kisses him. It’s not the same as kissing Armin, but it feels good. Bertholdt’s lips are soft and active, pressing against Eren’s mouth like waves meeting the shore.

His lips don’t linger for long, though. Bertholdt quickly moves to Eren’s jaw, down his neck. The touch raises goosebumps on his skin, his throat and collar bone so much more sensitive than he thought they’d be. Beretholdt’s hands fan out down Eren’s body, pushing his shirt up to feel along where he’s starting to gain solid muscle over his stomach. In a haze, Eren strips his clothes and throws another glance at Armin, who is barely keeping his eyes open. He’s watching Eren, his lips parted around his panting. Eren wants to kiss those lips.

Bertholdt positions himself on his hands and knees in front of Eren and flicks his gaze up. His face is about the same height as Eren’s hips, and Eren eventually puts the pieces together.

One hand guiding himself, Eren presses forward into Bertholdt’s waiting mouth. The heat is intense enough that Eren thinks his skin will sear off, but it feels so good. Once he’s inside, he threads his fingers through Bertholdt’s sweaty hair and moans shakily. He can’t believe he hasn’t done this with Armin already.

Like Reiner, Bertholdt bobs his head slowly, his tongue dragging over Eren’s shaft in a way he never knew would feel so good. Following instinct, Eren juts his hips forward every time Bertholdt leans in, and he watches with furrowed brows how his cock completely disappears in Bertholdt’s mouth. He’s in so deep, he thinks he feels the back of his throat.

“Does it hurt?” Eren asks in a rush. He wants to try.

He almost wishes he hadn’t said anything, because Bertholdt takes the wonderful sensation away when he leans back to answer.

“It can be uncomfortable, but it’s something you can get used to.” Bertholdt is looking at him when he says it, eyes round and lips wet. Like he’s possessed, Eren holds his cock and traces the tip around Bertholdt’s shining lips. When moisture beads out of the little hole at the top, Bertholdt swipes it away with his tongue.

He comes back in, letting Eren fill his mouth in a way that makes him dizzy. Next to them, Reiner lifts off of Armin one last time. Armin takes the chance to catch his breath, still hard between his legs. He hasn’t come yet, and despite how much he wants to, he knows there’s more to learn.

He watches Reiner grab the small bottle Bertholdt had brought and unstopper it.

“Women’s bodies get wet enough for a man to slide in comfortably,” he explains as casually as one would talk about the weather. “It’s too rough without something to make it wet, so if you can get your hands on some of this stuff, it’s much better.”

“What is it?” Armin asks, eyes following as Reiner tips the bottle upside down and pours out a bit of yellowish clear liquid.

“Olive oil. We swiped it from the kitchen.”

“Is that safe?” Armin chews on his bottom lip, thinking about Reiner using olive oil to make Armin wet enough to be penetrated.

“It’s not bad for you,” Reiner answers. He replaces the cork with one hand and sets the bottle down. The fingers of his other hand glisten with oil. “So unless you want to use ODM cleaner, or use nothing and probably bleed, then your best bet is to use this.”

He lowers his hand between Armin’s legs and presses two against his hole. Armin braces for the push like how Eren tried last week, with too much resistance and no give. Instead, Reiner gently circles the hole and spreads the oil around. It feels sticky, but that area on Armin’s body has never been touched like this, so it feels nice. Tingles prick along the top of his head and travel all the way down to his toes.

“Eren, pay attention,” Reiner orders.

Eren pulls himself back to the present moment, more than halfway to finding his release in Bertholdt’s mouth. But he slides out and watches, doing his best to ignore the needy pulse in his cock because what he’s about to see is something truly fascinating.

“If you find it too tight, you can use your fingers to help relax him,” Reiner instructs, his one finger teasing Armin’s hole and breaching it with little resistance.

Armin makes a sound that almost resembles pain, his face scrunching up around the feeling. It’s different, but it doesn’t hurt. Reiner said he needed to relax, so he tries, breathing through his mouth even as it falls open for an involuntary sound.

“Armin!” Eren calls.

“Nn… it’s okay, Eren…” Armin pants. His eyes open, and he stares blearily at the ceiling before scanning for Eren. His face is flushed down to the neck. “It feels good.”

“One at a time until you can fit your cock inside.” Reiner glances between Eren’s hips, where he’s still hard, and says, “Two should work for you, but I’m going to do three for myself.”

The comment would irritate Eren, but he hasn’t seen Reiner yet. Both he and Bertholdt still have all of their clothes on, and Eren is too enraptured by the sight of Armin to care.

“Watch, Eren,” Reiner barks again. “Watch his face when I aim for his navel.”

Reiner’s two fingers curl inside Armin, rubbing and massaging his walls so nicely that it makes Armin cry out. He throws his head to the side and fists the sheets, rocking his hips down to feel more of Reiner’s hand inside him. It’s his body doing it; his body knows exactly what he wants, and what he wants is this.

“Armin…” Eren whispers, too quiet for anyone to hear over Armin’s whimpering. He’s so hard, leaking onto the sheets and too amazed to be bothered to touch himself.

Reiner tosses the glass bottle to Bertholdt with his free hand.

“Eren,” Bertholdt says, ripping Eren’s attention away from Armin.

When Eren looks over, Bertholdt has already stripped his pants off, sitting up on his knees with his shirt barely reaching the tops of his hips. Despite himself, Eren blushes at the sight of Bertholdt’s flaccid cock hanging between his legs.

“Lie down,” Bertholdt instructs.

Eren does, stretching out on his back with his head close to Armin’s, facing the other direction. Reiner’s hand slows so Armin can breathe a little easier, though his hips keep twitching downward weakly.

When Eren is settled, Bertholdt swings one leg over his waist and straddles him. Eren’s body reacts to the proximity before his mind does, his cock throbbing in anticipation. Bertholdt holds out the uncorked bottle, and Eren offers his hand for him to pour some oil into his palm.

Like in a dream, Eren feels himself reach between Bertholdt’s legs, past his balls. He can’t exactly see what he’s doing, but he prods around for the hole he knows is there. Bertholdt gives an encouraging thrust downward when he finds it, mouth falling open. Eren’s eyes flick up to his face, and he catches Bertholdt looking at him with hooded eyes.

His first finger slides in easily, like the give of an overripe fruit. Eren blinks in surprise.

“That doesn’t hurt?” he asks.

“I’ve learned how to relax into it so it isn’t too tight,” Bertholdt answers, rocking down slowly to illustrate the point.

The feeling around his finger has Eren’s cock twitching in earnest. It’s hot and snug, made slippery with the oil. If it’s anything like Bertholdt’s mouth, Eren thinks he might not last long.

“Can you finish inside?” Eren blurts, a few steps ahead of himself.

“You can,” Reiner answers from somewhere behind him.

“I don’t want you to finish inside me, though,” Bertholdt adds quickly and sternly. “It’s a hassle to clean out.”

“Bertholdt doesn’t want to have your child,” Reiner comments with a snort. Bertholdt, Eren, and Armin go red at the suggestion.

“Put another finger in,” Bertholdt tells Eren, sending Reiner a shy glare.

Eren focuses on his hand, worming a second finger in alongside the first. The fit is marginally tighter, and he thinks back to Reiner’s comment about how many fingers he needs before he can put his cock in.

Reiner also adds another finger, easing Armin open with three. His fingers are thick like the rest of him, and Armin moans with a high voice. Eren’s ears feel hot with how close Armin’s voice is to him. Reiner has him gasping and whimpering with each movement, meanwhile Bertholdt has hardly uttered a sound.

“Aim for the navel,” Reiner tells Eren, like he heard his thoughts.

Eren imagines an invisible line connecting his fingers to the dimple on Bertholdt’s stomach and reaches for it. His walls are slippery and warm, something Eren struggles to describe having never felt anything like this with his fingers before. But his imagination must work, because Bertholdt suddenly jolts against his hand and grinds down, groaning low in his throat.

“Just like that,” Bertholdt breathes. Eren is sure he isn’t supposed to feel aroused just by the raspy sound of another man’s voice, but he is all the same.

He continues to reach for the same spot inside until Bertholdt grows stiff between his legs. He takes Eren’s cock in his hand and lines it up with his own, strumming them together just like he and Armin do sometimes. His hand is slick with oil, and it coats both of them with each stroke of his hand. Bertholdt’s hips are doing most of the work now, riding against Eren’s hand while Eren does little but watch in fascination.

“Reiner, I’m going to…” Bertholdt says, lifting himself off Eren’s fingers. He doesn’t finish the thought, only angles himself and Eren’s cock, and Eren can fill in the rest.

Where he and Armin had to stop short last time, Bertholdt keeps pressing until Eren breaches him. Whatever Eren had felt on his fingers, it’s so much more intense when Bertholdt sinks down and envelopes him from tip to root. Inside is so hot. Eren’s eyes roll to the ceiling, and his hands involuntarily cling at Bertholdt’s hips like he might fly off the bed if he doesn’t. Usually, Eren can keep quiet, but a moan rips out of him before he even knows it’s building. He plants his feet on the bed and jerks upward into the waiting heat of Bertholdt’s body.

Reiner watches when Eren slides in and finds his rhythm. He’s over enthusiastic and a bit rough, just like how he tackles every aspect of his life, but Bertholdt can handle him. When they establish a pace together, Bertholdt bouncing up and down on Eren’s hips, Reiner retracts his fingers and steals the well-used bottle for himself.

Armin watches through his lashes, feeling already worn out but so ready for more. Reiner pulls himself out of his pants and lathers the oil over the length. Armin swallows thickly at the size, his own thoughts surprising him when he realizes how badly he wants it. His body isn’t built like a woman’s, but it’s reacting to the thought of a man entering him like it’s the most natural phenomenon in the world.

Reiner catches the look in his eyes and pauses, resting a hand on Armin’s bent knee.

“You can tell me to stop at any time,” Reiner assures him.

Armin’s eyelashes flutter, and he’d blush if he wasn’t already pink from the ears down. “It’s not that,” he promises, and he searches for the right words. “You’ve been doing all the work.”

“It’s easiest when you’re on your back.” Reiner presses his thumb to Armin’s inner knee, rubbing gently. “Why don’t you get on your hands and knees, then? You can watch Eren that way.”

Reiner helps him roll over and lift off the bed. Armin gets his first non-upside-down view of Eren since they began, and the veins in his neck pop with the ordeal of having Bertholdt bouncing in his lap. Armin’s fingers curl into the blanket below him, enraptured by the movement of Bertholdt and Eren’s bodies together.

Behind him, Reiner lays a hand on his hip, and something hard and wet pokes at his hole. Reiner’s fingers had done the trick of preparing him for what it would feel like, so when Reiner pushes forward, Armin is ready to accept him as his cock splits him open.

“Ahn…” The sound that leaves Armin’s throat is unwarranted, but he has no control over it. The sensation filling him is so new and so hot that he can’t help the way he pushes back against Reiner, searching for more and more until he feels Reiner bump up against the backs of his thighs. Reiner was right about being on his hands and knees; he can be much more active like this, seeking out the next thrust before it comes.

Reiner is quick to pick up the pace. He holds Armin with both hands and pulls him back, their skin slapping together. Armin lets out a sound that could be close to a scream, and he arches his back to search for that feeling again. He likes the tight hold around his hips, and he catches himself hoping there will be bruises later.

Eren twists his neck to glower at Reiner. "You're being too rough with him!" he scolds, but Reiner's only response is to lock eyes with him and thrust hard into Armin.

"It's okay, Eren." Armin pants, swallowing hard. He manages a smile through the haze descending upon him. "It feels so good." It's the second time he's had to console Eren's concern, but Armin is touched Eren worries so much about him. He is right there, and Armin misses him so much. His heart splinters open with so much want, even with Reiner taking him from behind and Bertholdt claiming Eren from on top.

They’re just a few inches apart from each other, and Eren shuffles until he can angle himself even closer. With his hands still on Bertholdt’s hips and probably bruising, Eren finds himself between Armin’s hands, staring up at the flushed face and mussed hair above him.

Armin’s eyes are dark in a way Eren has seen only a few times before. Dark with desire and hunger, and it sends a shudder down Eren’s spine.

“Armin,” he whispers.

One of his hands leaves Bertholdt’s hip to cup behind Armin’s neck, pulling him down. Armin drops to his elbows, one arm on each side of Eren’s head, and kisses him. They’re both breathless, but they continue on like they don’t need air, kissing upside down of each other. Armin sends a moan down his throat, and Eren drinks it up before giving one back in return. Armin’s tongue finds its way into Eren’s mouth. Eren grips tighter to Bertholdt and holds him down so forcefully that Bertholdt struggles to lift back up on his knees to continue their rhythm. Eren is so hard; he needs to find his release soon or he thinks he might go mad.

“E-Eren…” Bertholdt’s voice cracks around a moan. He presses his fingers against Eren’s abdomen and breaks free of his hold, slowing his bouncing down to catch his breath. Eren hardly notices, too wrapped up in Armin.

“I want it to be you,” Eren grates against Armin’s trembling lips, nails scratching at the back of his neck.

“I want you too,” Armin whispers back, then twists his head to look behind him. “Reiner…” he calls, interrupted but a hard thrust and his own resulting moan. “Ah, Reiner—can we switch?”

He’s so close without having been touched anywhere but his ass, and he wants to reach completion with Eren inside him.

Reiner slows and pulls out, the feeling so strange and arousing that Armin chokes around a surprised gasp. He is immediately left feeling too empty, and he vaguely wonders if he’ll ever feel normal again without something filling him, now that he knows how good this feels.

“I was starting to lose it, watching Eren fuck Bertholdt like that,” Reiner says nonchalantly. He goes to sit with his back against the wall and stretches one hand out. Bertholdt takes his hand wordlessly and allows himself to be pulled off of Eren and into Reiner’s lap. Like two spoons fitting together perfectly, Bertholdt slides his legs around Reiner and sinks down on him. Reiner trails his hands reverently up Bertholdt’s back, sighing against his mouth when they kiss.

Eren sucks in a breath when the heat leaves his cock so suddenly. He watches, almost mournfully, as Reiner and Bertholdt continue on like he and Armin aren’t even there, but he’s pulled from his thoughts by a gentle hand on his chest.

Angling his head, Eren looks up at Armin, who’s still panting lightly and beckoning him forward with nothing but a look. Scrambling to his hands and knees, Eren closes the distance between them and presses his mouth greedily against Armin’s. Humming, Armin cups his cheek and leads him backward, until he’s laying with his head against the pillow and Eren is crawling between his legs. This is more familiar.

Eren clutches Armin’s thigh where it rides up his waist and adjusts his hips. It’s clumsy without the use of his hands, but Armin is wide and open enough for him to find the mark without looking. When Eren slips into Armin, it’s like he’s meant to be there, and they both breathe in what feels like relief as Eren moors up until there’s nothing left to give.

Armin is still kissing him, both hands holding his cheeks. They fit together like two puzzle pieces, movement and rhythm coming so easily to both of them. It seems like every thrust lands Eren exactly where Armin needs him, and his moans reach a crescendo that feels like it’s been forever in the making. All sounds drown out until it’s just them in a bubble, so wrapped up in each other as snugly as Armin’s legs wrap around Eren’s waist. Even Reiner and Bertholdt, just two feet away from them, fade out of existence for a blissful moment as a wave crashes over Armin and Eren in succession.

They reach climax one after the other, and it’s anyone’s guess who was first. Without really meaning to, Eren spills into Armin’s waiting body before he knows it’s happening. He buries himself as deep as he can go and stays there, wants to always stay there, until his cock is done pulsing and his ears stop ringing.

Armin doesn’t know what Bertholdt was talking about. Being filled by Eren like this, at the moment of completion, might be the best thing he’s ever felt. He floats back to himself in the moments after his release, coming to realize he’s wrapped his arms around Eren’s neck rather tightly. Eren’s face is buried in his shoulder, and they’re both breathing rapidly. Armin’s heart hammers in his chest, or maybe it’s Eren’s. Or maybe they are one being with one beating heart for a few unreal moments.

In the moments that follow, they start to feel how sweaty they’ve gotten. Eren’s limbs protest when he tries to sit up, and separating from Armin is excruciating, but he props himself up on shaky arms and looks down. Painting Armin’s stomach and chest is a mess, but it’s beautiful. Eren gives one shift of his hips and feels the matching mess inside Armin’s body. As much as he wants to stay inside, he’s softening, and he eventually slips out against his wishes.

Armin feels as if his lower half is sloshing like water in a cup, and he’d blush if he had it in him. Above him, Eren looks so beautiful and worn out that Armin can forget about their responsibilities for the rest of the day and dream about holding him until they drift off. He certainly forgets about their bedmates until he hears a moan and a gasp, and he puts the pieces together that Reiner and Bertholdt have finished as well.

Armin reaches up and touches Eren’s cheek. Eren leans into it, then turns his head to press a kiss to Armin’s wrist. He follows the line of his arm all the way up, peppering more and more kisses until their lips meet again. Armin hums contentedly, arms falling around Eren’s neck again.

Eren feels like, if given enough time, he could do it all over again, this time only with Armin from start to finish. They have so much to make up for, having only just learned this is what it’s like to truly be together. Heat in his lower belly stirs again, and judging by the way Armin’s legs seem to spread open on their own, he’s not the only one.

It’s ruined when Reiner kicks at Eren’s heel with his foot. Reluctantly, he separates from Armin, leaving a peck on the tip of his nose before turning around. Reiner has tucked himself back into his pants, looking like nothing out of the ordinary. Bertholdt is sufficiently red and in the process of peeling his pants back over his sweaty legs.

“You have an hour until the lieutenant comes by to check on your cleaning job,” Reiner reminds them. He glances pointedly down between Armin’s legs, where everyone can see and Armin can very much feel fluid leaking out of him. “I’d use that time to clean yourselves up, then get to work actually cleaning the barracks.”

“Five more minutes,” Eren groans, plopping his entire body onto Armin and nuzzling into his neck. “Aren’t you two supposed to be on manure right now?”

“I would have liked to not think about that so soon after we’ve had sex,” Bertholdt groans, scrubbing a hand over his face.

Armin giggles, turning his nose into Eren’s hair. They both smell horrendous, and showers will have to wait until tonight, but he couldn’t care less about any of that.

“Hey, Armin,” Eren whispers theatrically loudly. “Next time, let’s switch.”

Armin hums, stroking up and down his back. “When is next time?”

“As soon as possible,” Eren answers vehemently.

“Hey. Don’t get any ideas about doing this after dark. Some of us have to share these barracks with you, and we like to sleep,” Reiner warns. Armin and Eren just laugh louder.

“Thank you for helping us,” Armin says when Bertholdt and Reiner start to climb out of the bunk. “You didn’t have to do that.”

Hanging over the edge, Reiner pauses to look up at them. “If you’ve found someone you love inside these god-forsaken walls, you better make damn sure you hold onto them as tightly as you can.”

**Author's Note:**

> i've been in this fandom since the beginning and i can't believe this is the first fic i've written for it. hope you enjoyed! you can find me on [twitter](https://twitter.com/shamu_who) retweeting sad eruri art, among other things


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